The effect of dexmedetomidine on remifentanil induced postoperative hyperalgesia in patients undergoing thyroidectomy

Abstract

Objective To observe the effects of dexmedetomidine (Dex) on postoperative mechanical pain threshold,and to identify whether Dex can prevent postoperative hyperalgesia induced by remifentanil.Methods we taked the completely random grouping method.60 patients undergoing elective Thyroidectomy were randomly divided into three groups:Dex group (HD group):The patients received Dex 1.0 μg/kg in 10 min before induction of anesthesia,then given 0.4 μg·kg-1·h-1 continuous infusion of Dex until 1 h before the end of surgery together with the continuous infusion of remifentanil 0.2 μg ·kg-1 ·min-1.Low dose remifentanil group (LO group) and high dose remifentanil group (HI group):The patients received normal saline infusion replaced Dex,then given remifentanil 0.05 μg·kg-1 ·min-1 and 0.2 μg·kg-1 ·min-1 respectively.Mechanical pain thresholds on forearm and periincisional area were assessed by yon Frey filament.Mechanical pain thresholds were recorded before surgery,and at 2,4,8,12,24,48 h postoperation,additional visual analogue scale(VAS) score and postoperative adverse reactions within 48 h were recorded.Results Mechanical pain threshold described by the median,interquartile range (M±QR),Compared with mechanical pain thresholds on forearm with the preoperative(13±43),mechanical pain thresholds in the HI group at 2 h(10±28),4 h(11±22),8 h(8±14),12 h(6± 25),24 h(8±18),48 h(8±19) are significantly decreased(P＜0.05),In the HD group at 8 h(16±58),12 h(22±63),24 h(30±72),48 h(20±109),compared with the preoperative(10±20),the mechanical pain thresholds are significantly increased(P＜0.01),In the LO group,the mechanical pain thresholds are decreased when compared with the preoperative,but the difference was not statistically significant(P＞0.05).The HD group(16±58),(22±63),(30±72) are higher at 8,12,24 h compared with the HI group(8±14),(6± 25),(8±18)(P＜0.05),HI group compared with the LO group (15±45),(19±32),(17±24),(13±33),(16±21),(15±26) is significantly lower in the postoperation (P＜0.01).The change in pain threshold on the periincisional area was similar among the groups.Additional VAS values compared with preoperative were significantly increased (P=0.004),but VAS value compared among the three groups is not statistically significant.Conclusions The application of Dex in Thyroidectomy can increase postoperative mechanical pain threshold,which can prevent remifentanil induced postoperative hyperalgesia. Key words: Dexmedetomidine ; Remifentanil; Mechanical pain threshold